Our invention relates generally to an apparatus for the transfer (reading and/or writing) of data with disklike record media such as magnetic disks notably including those of the "fixed" or hard disk variety. More particularly, our invention pertains to a positional control system for a data transducer or head in such an apparatus in accessing the transducer to any of a multiplicity of concentric data tracks on the rotating disk. The transducer position control system of our invention particularly features provisions for protection of the apparatus against shocks or vibrations that may be exerted thereon in use.
Hard disk drives in general employ some form of rotary or linear actuator under closed- or open-loop electronic control for positioning the transducer in centerline alignment with any of the data tracks on the disk. Hertrich et al. U.S. Pat. No. 4,390,912 teaches a servo positioning system incorporating a voice coil motor.
One of the problems that have been left unsolved in connection with such transducer positioning systems is how to position the transducer in the face of vibrations or shocks that may be applied to the disk drive in use. Transducer displacement due to such external forces has been particularly liable to occur if the positioning system employs a voice coil motor. Although generally preferred for its high response, the voice coil motor inherently lacks in the capability of holding the transducer against lateral displacement from any desired data track on the disk.
Let us suppose that the transducer is mechanically displaced from one track to another on which data has been written. The transducer has been allowed to overwrite, and so destroy, the data on the neighboring track in the prior art system of the type under consideration, if a write current is fed to the transducer before its lateral position is corrected under servo control. The user has been warned of this danger and advised not to subject the disk drive to shocks or vibrations. Hard disk drives have thus been intended for use in fixed locations only. Obviously, then, they will find their way into portable computer systems if protected against data error or destruction due to external shocks or vibrations.